1. Field of the Invention
The present invention relates to the field of liquid crystal displaying, and in particular to a curvature-adjustable backplane and liquid crystal display device having the backplane.
2. The Related Arts
Liquid crystal displays (LCDs) have a variety of advantages, such as thin device body, low power consumption, and being free of radiation, and are thus of wide applications, such as liquid crystal televisions, mobile phones, personal digital assistants (PDAs), digital cameras, computer monitors, and notebook computer screens.
A liquid crystal display generally comprises an enclosure, a liquid crystal panel arranged in the enclosure, and a backlight module mounted in the enclosure. The principle of operation of the liquid crystal panel is that liquid crystal molecules are arranged between two parallel glass substrates and a plurality of vertical and horizontal tiny electrical wires are arranged between the two glass substrates and electricity is applied to control the liquid crystal molecules to change direction in order to refract light emitting from the backlight module to pass through a pixel structure formed on the glass substrates to generate a color image. The backlight modules can be classified in two types, namely a side-edge backlight module and a direct backlight module, according to the site where light gets incident. The direct backlight module comprises a light source, such as a cold cathode fluorescent lamp (CCFL) or a light-emitting diode (LED), which is arranged at the backside of the liquid crystal panel and light is homogenized by a diffusion plate to form a planar light source supplied to the liquid crystal panel. The side-edge backlight module comprises an LED light bar, serving as a backlight source, which is arranged at an edge of a backplane to be located rearward of one side of the liquid crystal panel. The LED light bar emits light that enters a light guide plate (LGP) through a light incident face at one side of the light guide plate and is projected out of a light emergence face of the light guide plate, after being reflected and diffused, to pass through an optic film assembly so as to form a planar light source for the liquid crystal panel.
Recently, with the progress of the displaying technology, major manufacturers have marketed curved display devices, such as curved televisions, one after another. Generally speaking, the curved display devices allow for the best viewing effect from edge to edge, while a regular display device has poor capability of displaying at edges of a screen. The curved display devices have a screen that is entirely of a curved design to provide a wide full-view image, allowing for the same visual enjoyment at both the central portion and the circumferential portion of the screen and also reducing distortion of off-axis viewing for viewing at a short distance. Further, the curved display devices allow a viewer's viewing distance to be extended, achieving better experience of viewing. Thus, compared to the regular display devices, the curved display devices have advantages, including: (1) brand differentiating, (2) wider viewable angle, and (3) reducing distortion for short distance viewing.
The conventional ways of forming a curved liquid crystal display generally include: (1) mounting a support rack having a specific curve to a backplane to force the backplane to deform into a curve consistent with that of the rack; and (2) directly forming a structure of a curved surface on the backplane. However, a backplane formed with either one of these ways is generally curved with a fixed curvature and thus the curvature of a display device obtained with the two ways is fixed. No adjustment of the curvature is available to suit users' need of watching or to allow for switching between a planar display device and a curved display device, whereby the view angle is subjected to undesired constraint.
A thermal bimetal is a composite material composed of two (or more) metal layers or alloy layers having different thermal expansion coefficients that are securely bonded together. One of the layers has a lower thermal expansion coefficient and is a passive layer. The other layer has a higher thermal expansion coefficient and is an active layer. The active layer and the passive layer both have relatively high internal resistances. When electricity is applied to the thermal bimetal, the active layer and the passive layer generate a great amount of heat quickly, leading to a rise of temperature. The deformation of the active layer resulting from thermal expansion is apparently greater than the deformation of the passive layer resulting from thermal expansion and this makes the thermal bimetal to curve toward the side of the passive layer. Due to the thermal bimetal being sensitive to temperature and showing a characteristic that the amount of curving deformation can be controlled through controlling the temperature, the thermal bimetal can be used to make a backplane of a liquid crystal display device, wherein adjustment of the curvature of the liquid crystal display device or switching between a planar display and a curved display can be achieved through controlling the curvature of the backplane. However, as shown in FIG. 1, a conventional curvature-adjustable backplane made of a thermal bimetal suffers certain drawbacks, which are that since the lengthwise and widthwise dimensions of a liquid crystal display device are relatively great and a backplane 10 made of a thermal bimetal has a relatively small aspect ratio L′/W′, in the process when the backplane 10 is subjected to heating and thus deformation, obvious curving and deformation occurs in all the directions so that it is not possible for the liquid crystal display device to achieve a precise adjustment of the curvature thereof and thus it is not possible to achieve a desired curved condition.